Critical AWS SSM Agent Vulnerability Exposes EC2 IAM Credentials
A critical flaw in the AWS Systems Manager (SSM) Agent (CVE-2026-89049) allows authenticated attackers to bypass Session Manager port-forwarding restrictions, access link-local services, and steal temporary IAM credentials from Amazon EC2 instances. The vulnerability affects SSM Agent versions prior to 3.3.4851.0 and is rated critical (CVSS v3.1) due to its low attack complexity, minimal privilege requirements, and high impact.
Vulnerability Details
The flaw resides in the AWS-StartPortForwardingSessionToRemoteHost capability, which is designed to enable secure remote management without exposing SSH/RDP. However, the agent failed to properly validate alternative IP address representations, allowing attackers to bypass denylists and tunnel traffic to link-local addresses including the EC2 Instance Metadata Service (IMDS) at 169.254.169.254.
Exploiting this Server-Side Request Forgery (SSRF) weakness (CWE-918, CWE-1289), an attacker with ssm:StartSession permissions could query the IMDS and extract temporary IAM credentials from an EC2 instance’s attached role. These credentials could then be used to perform AWS API calls, with the potential impact depending on the role’s permissions such as accessing S3 buckets, Secrets Manager, IAM resources, or databases.
Exploitation & Impact
While exploitation requires authenticated access and Session Manager permissions, the risk is significant given that SSM access is often granted to developers, operations teams, automation accounts, and third-party support. A compromised instance could serve as a proxy for internal network access, leading to broader cloud account compromise.
Mitigation & Response
AWS has released SSM Agent version 3.3.4851.0 to patch the vulnerability. Organizations should:
- Upgrade affected instances immediately.
- Restrict access to the AWS-StartPortForwardingSessionToRemoteHost SSM document.
- Limit ssm:StartSession permissions to trusted administrators and tightly scoped roles.
- Monitor CloudTrail logs for unusual Session Manager activity, including unexpected port-forwarding sessions.
Failure to address this flaw could expose sensitive IAM credentials and enable lateral movement within AWS environments.
Source: https://cyberpress.org/critical-aws-flaw/
Amazon Web Services TPRM report: https://www.rankiteo.com/company/amazon-web-services
"id": "ama1789374268",
"linkid": "amazon-web-services",
"type": "Vulnerability",
"date": "9/2026",
"severity": "85",
"impact": "4",
"explanation": "Attack with significant impact with customers data leaks"{'affected_entities': [{'location': 'Global',
'name': 'AWS Customers',
'type': 'Cloud Service Users'}],
'attack_vector': 'SSRF (Server-Side Request Forgery)',
'data_breach': {'data_exfiltration': 'Possible if credentials are misused',
'sensitivity_of_data': 'High (temporary IAM credentials with '
'potential AWS resource access)',
'type_of_data_compromised': 'IAM credentials'},
'description': 'A critical flaw in the AWS Systems Manager (SSM) Agent '
'(CVE-2026-89049) allows authenticated attackers to bypass '
'Session Manager port-forwarding restrictions, access '
'link-local services, and steal temporary IAM credentials from '
'Amazon EC2 instances. The vulnerability affects SSM Agent '
'versions prior to 3.3.4851.0 and is rated critical (CVSS '
'v3.1) due to its low attack complexity, minimal privilege '
'requirements, and high impact.',
'impact': {'data_compromised': 'Temporary IAM credentials',
'identity_theft_risk': 'High (if IAM credentials are misused)',
'operational_impact': 'Potential unauthorized AWS API calls, '
'lateral movement within AWS environments',
'systems_affected': 'Amazon EC2 instances with SSM Agent versions '
'prior to 3.3.4851.0'},
'post_incident_analysis': {'corrective_actions': 'Patch SSM Agent to version '
'3.3.4851.0 or later',
'root_causes': 'Improper validation of alternative '
'IP address representations in '
'AWS-StartPortForwardingSessionToRemoteHost'},
'recommendations': ['Upgrade affected SSM Agent instances immediately',
'Restrict SSM Session Manager permissions',
'Monitor for unusual port-forwarding activity'],
'references': [{'source': 'AWS Security Advisory'}],
'response': {'containment_measures': 'Upgrade to SSM Agent version 3.3.4851.0',
'enhanced_monitoring': 'Monitor CloudTrail logs for unexpected '
'port-forwarding sessions',
'remediation_measures': ['Restrict access to the '
'AWS-StartPortForwardingSessionToRemoteHost '
'SSM document',
'Limit ssm:StartSession permissions to '
'trusted administrators and tightly '
'scoped roles',
'Monitor CloudTrail logs for unusual '
'Session Manager activity']},
'title': 'Critical AWS SSM Agent Vulnerability Exposes EC2 IAM Credentials',
'type': 'Vulnerability Exploitation',
'vulnerability_exploited': 'CVE-2026-89049'}